JPH0511712B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a high-power underwater ultrasonic transducer that is broadband and omnidirectional.

(Prior Art) Conventionally, as a transducer having omnidirectional properties, a cylindrical piezoelectric ceramic transducer that operates in a radial expansion vibration mode (radial extensional mode) as shown in Fig. 6 has been widely used. It is used. This transducer has silver or gold baked electrodes 61 on the inner and outer surfaces.
62 is formed, and a DC high electric field is applied between the electrodes 61 and 62 to perform polarization treatment radially in the thickness direction as shown by the arrows. This transducer operates in a so-called diameter expansion vibration mode in which the diameter expands and contracts uniformly by applying an alternating current voltage from the electrical terminals 63 and 64. Omnidirectional acoustic radiation is performed from the

(Problems to be Solved by the Invention) Conventional cylindrical piezoelectric ceramic transducers can radiate sound omnidirectionally with respect to the central axis, but they have the following problems. 6th
As is clear from the figure, all conventional transducers are made of piezoelectric ceramics. Piezoelectric ceramics has a density of approximately 8.0×10 ³ Kg/m ³ and the sound velocity related to the diameter expansion mode is 3000 to 3500 m/sec, so the specific acoustic impedance (defined as the product of density and sound velocity) is 24× ¹⁰⁶ ~28× ¹⁰⁶
The characteristic acoustic impedance of MSKrayls is nearly 20 times that of water, which is the medium, and is extremely large. This results in an acoustic impedance mismatch between the water and the transducer, limiting the available bandwidth to 15 percent to no more than 30 percent. Therefore, for example, when a conventional transducer is used in a sonar system, the narrowband characteristic causes a long pulse tail and degrades the distance resolution. In general, a broadband transducer is indispensable in order to obtain compact pulse response characteristics with little pulse tailing. In order to obtain a broadband cylindrical piezoelectric ceramic transducer, the mechanical impedance of the transducer should be reduced (this is the mass of the transducer per acoustic radiation area) in order to improve the impedance matching with water. )
was necessary, and the only solution was to reduce the conventional wall thickness. However, when the wall thickness of the transducer is made thinner, processing of the piezoelectric ceramic becomes difficult, and the mechanical strength deteriorates significantly, making high-power acoustic radiation impossible.

An object of the present invention is to realize an omnidirectional transducer that has wide-band, highly efficient acoustic radiation characteristics and is capable of high-power transmission.

(Means for Solving the Problems) The basic configuration of the transducer according to the present invention includes a cylindrical piezoelectric transducer that operates in an expanding vibration mode, and a cylindrical acoustic radiator that also operates in an expanding vibration mode. The cylindrical piezoelectric transducer and the cylindrical acoustic radiator are arranged in series so that their central axes coincide with each other, and include a flexible connector for coupling the cylindrical piezoelectric transducer and the cylindrical acoustic radiator.

The transducer of the present invention has two resonance modes as a whole, namely a common mode with a low resonance frequency (a vibration mode in which the cylindrical piezoelectric transducer and the cylindrical acoustic radiator are in phase) and a high resonance mode with a high resonance frequency. There is an anti-phase mode (a vibration mode in which the cylindrical piezoelectric transducer and the cylindrical acoustic radiator are in anti-phase), and acoustic radiation can be strongly emitted between the frequencies of these two modes. , an omnidirectional ultrasonic transducer with broadband characteristics.

(Function) FIG. 1 shows a typical example of a non-directional high-power underwater ultrasonic transducer according to the present invention. In the perspective view shown in FIG. 1, 10 is a cylindrical piezoelectric transducer, 13 is a cylindrical acoustic radiator, and 14 is a flexible connector. 10 is a cylindrical piezoelectric transducer,
It is made up of a piezoelectric ceramic cylindrical vibrator 12 on the inside and a cylinder 11 made of metal or fiber-reinforced composite material on the outside, and 12 and 11 are firmly bonded with adhesive. This piezoelectric ceramic cylindrical vibrator 1
For example, electrodes are provided on the upper and lower surfaces, or electrodes are provided on the inner and outer circumferential surfaces, for example.
Piezoelectricity can be imparted to these electrodes by polarization treatment, and both have transverse effects31
It is possible to strongly excite mode diameter expansion vibration. In addition, when exciting radial expansion vibration in the longitudinal effect 33 mode, as is well known, the piezoelectric ceramic cylinder is divided radially on a plane perpendicular to the circumference, and the resulting divided planes are perpendicular to the circumference. This can be easily carried out by forming an electrode on the electrode, performing polarization treatment using this electrode, and then driving with this electrode.

In the cylindrical piezoelectric transducer 10, it is essential that the piezoelectric ceramic cylindrical vibrator 12 and the cylinder 11 are integrated to perform radial expansion vibration. It is desirable to keep compressive bias stress constantly applied to. This is because piezoelectric ceramics are brittle against tension, and the strength against tension is a fraction of the strength against pressure. Therefore, in the diameter expansion vibration mode, if the 12 parts expand uniformly, it is difficult to prevent destruction. Because you can. For this reason, the following measures have been taken in the piezoelectric transducer 10 portion of the transducer according to the present invention. That is, a cylinder made of metal or fiber-reinforced composite material is a piezoelectric ceramic cylindrical vibrator 1.
The coefficient of thermal expansion is one order of magnitude larger than that of cylindrical 1.
An adhesive is applied to the inner adhesive surface of the vibrator 1 and the vibrator 12 is bonded to the vibrator 12. As a result, at normal operating temperatures, compressive bias stress is always applied to the piezoelectric ceramic cylindrical vibrator 12, making it possible to drive with a much larger amplitude than conventional cylindrical piezoelectric ceramic vibrators. .

In addition, the cylindrical acoustic radiator 13 is made of a fiber-reinforced composite material that is lightweight to facilitate broadband matching with water, and has high rigidity against bending deformation to achieve uniform diameter expansion vibration. or Al,
An alloy mainly composed of Mg or a composite of multiple layers of these materials is desirable.

The flexible connector 14 is made of a high-strength metal material, e.g.
Al alloys, Mg alloys, Ti alloys, steel alloys or fiber reinforced composite materials are preferable. Also, 11,1
It goes without saying that parts 4 and 13 can also be constructed as one piece.

Next, the principle of operation of the transducer of the present invention will be explained. As mentioned above, the transducer according to the present invention has two modes of vibration: an in-phase mode and an anti-phase mode. The in-phase mode is a vibration mode in which when the transducer 10 expands in the radial direction as shown by the solid double arrow, the acoustic radiator 13 also expands in the radial direction as shown by the solid double arrow. At this time, the flexible connector 14 undergoes almost no deformation. In the reverse phase mode, converter 10
This is a vibration mode in which the acoustic radiator 13 uniformly contracts in the radial direction as shown by the dotted double arrow when the acoustic radiator 13 expands uniformly in the radial direction as shown by the double arrow with a solid line. A bending deformation is performed as shown in FIG. 2 in which both the joint with the converter 13 and the joint with the transducer 10 are roll ends. Compared to the in-phase mode, in the anti-phase mode, bending deformation occurs in the coupler 13, and the resonance frequency becomes higher by the bending stiffness of the coupler 13. That is, there are an in-phase mode and an anti-phase mode that have different resonance frequencies. It goes without saying that when the cylindrical piezoelectric vibrator 10 is uniformly contracted in the radial direction, the direction of vibration displacement in the acoustic radiator 13 is opposite to the direction of the double arrow in FIG.

The equivalent circuit of the transducer according to the present invention can be represented by a lumped constant approximate equivalent circuit shown in FIG. As is clear from FIG. 3, the transducer according to the present invention is completely different from the conventional single resonant transducer, and is a bandpass filter that uses water as the acoustic load.
In FIG. 3, C _d is the damping capacity, -C _d appears when a longitudinal effect ceramic vibrator is used, and -C _d does not appear in a transverse effect vibrator.
A is the force coefficient, m and c are the equivalent mass and equivalent compliance of the cylindrical piezoelectric vibrator 10, m ₂ ,
c ₂ is the equivalent mass of the cylindrical acoustic radiator 13, respectively;
equivalent compliance, c _c is the flexural compliance of the flexural coupler, S _a is the acoustic radiation cross section, and Z _a is the acoustic radiation impedance of the water in the acoustic system.

In this transducer, the flexible connector 14
A cylindrical piezoelectric vibrator 10 and an acoustic radiator 1 are sandwiched between
In addition to transducers (m ₁ = m ₂ , c 1 = c 2 ), which have the same equivalent mass and resonant frequency (m 1 = m 2 , c ₁ = c ₂ ), the equivalent mass and resonant frequency can be determined by making full use of the asymmetric operating parameter method or transformer filter theory. It goes without saying that different asymmetric underwater ultrasonic transducers (m ₁ =m ₂ , c ₁ =c ₂ ) can be constructed.

Another example of the structure of the transducer according to the present invention is shown in FIG. This is a cylindrical acoustic radiator 1
At both ends of 3, via flexible connectors 14,
By arranging two cylindrical piezoelectric vibrators 10 and driving the two vibrators 10 in the same phase, it is possible to obtain a broadband and omnidirectional high-power transducer.

(Example) An example of a transducer based on the present invention is shown in FIG. In FIG. 5, numeral 12 is a piezoelectric ceramic cylinder polarized in the thickness direction, and silver baked electrodes are formed on the inner and outer peripheral surfaces of the cylinder. Also, 1
Reference numeral 1 is a cylinder made of Al alloy, which is firmly bonded at a temperature of 150° C. via an epoxy adhesive according to the method described above. Therefore, at room temperature, a compressive bias stress is always applied to the piezoelectric ceramic. 14 is a flexible connector, and 51 is an inner cylinder of the acoustic radiator 13 portion. 11, 14, 5
One part is made of the same Al alloy and is integrated. Further, 52 is a carbon fiber reinforced resin (C-FRP) having an epoxy resin matrix in which fibers are arranged in the longitudinal direction of the cylindrical acoustic radiator 13, and a C-FRP sheet in which carbon fibers are arranged in only one direction. Al alloy cylinder 51 is attached via epoxy adhesive.
It is wrapped around to form an outer cylinder. Further, the outer surface of the cylinder 52 is wrapped with glass fiber along the cylindrical direction, and a compressive bias stress is always applied to the cylindrical acoustic radiator to increase the adhesive strength between parts 51 and 52. In this case, it goes without saying that in addition to glass fibers, reinforcing fibers such as carbon fibers and aramid fibers can also perform the same function. As a result, in the acoustic radiator 13, the portions 51 and 52 vibrate together in a radial expansion vibration mode, and acoustic radiation can be strongly radiated from the outer surface of the acoustic radiator 13. In addition, in the present acoustic radiator 13, the fiber direction of the C-FRP cylinder 52 is the longitudinal direction of the cylinder (0-0' direction).
Therefore, this acoustic radiator 13 has a significantly large bending rigidity in the longitudinal direction, and cylindrical bending hardly occurs in the frequency body actually used. On the other hand, in the circumferential direction, since no fibers are arranged other than a few reinforcing fibers wound around the outside of the cylinder 52, the C-FRP cylinder 52 functions to lower the resonance frequency of the acoustic radiator 13. Regarding the radial vibration mode, the sound velocity of Al alloy is about 40% higher than that of piezoelectric ceramics. C-
The sound velocity regarding the radial vibration mode of the FRP cylinder 52 is:
This speed of sound is almost equal to that of epoxy resin, which is the matrix, and is about 40% lower than that of piezoelectric ceramics. Therefore, the acoustic radiator 1
3, by changing the thickness ratio of the Al alloy cylinder 51 part and the C-FRP cylinder 52 part, the resonant frequency of the radial vibration mode of the acoustic radiator 13 can be adjusted, resulting in an optimal design for manufacturing. It has the advantage that it can be easily adjusted to the desired value.

This transducer covers the outer surface of the cylindrical vibrator 10 with Kirk rubber, which is an acoustic decoupling material, and uses the well-known watertight technology. Watertightness is maintained by covering the lid with a disc and molding it with neoprene rubber. The external dimensions of the prototype transducer are 15.8 cm in height and 10.5 cm in diameter.

In the transducer of this example, there are two resonance modes: in-phase mode and anti-phase mode.
Because it can utilize two resonances, it has a significantly wider band than conventional transducers, and because it uses lightweight materials such as Al alloy and C-FRP as the acoustic radiator, it can match broadband acoustics. Because this transducer is easily reachable and is based on high-strength materials such as Al alloy, this transducer has a broadband high power output with a specific bandwidth of over 60% and an output sound pressure of over 190 dBre 1 μPa at 1 m. Wave transmission can be performed extremely easily,
Because it has excellent acoustic matching with water, a highly efficient transducer can be realized. Note that the formation of the cylinder 52 is a desirable form and is not an essential element. It is also possible to form the flexible connector 14 directly on the piezoelectric ceramic cylindrical vibrator 12.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to provide an omnidirectional underwater ultrasonic transducer that has a wide band, high efficiency, and excellent high power characteristics.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of the omnidirectional underwater ultrasonic transducer according to the present invention, Fig. 2 is a diagram showing the operation of the flexible connector used in the transducer of the present invention, and Fig. 3 is a diagram showing the operation of the flexible connector used in the transducer of the present invention. An equivalent circuit diagram of a transducer, FIG. 4 is a diagram showing another configuration example of a transducer based on the present invention, FIG. 5 is a diagram showing an embodiment of a transducer based on the present invention, and FIG. is a diagram showing a conventional omnidirectional underwater ultrasonic transducer. In the figure, 10 is a cylindrical piezoelectric transducer, 11 is a cylinder made of metal or fiber reinforced composite material, 1
2 is a piezoelectric ceramic cylindrical vibrator, 13 is a cylindrical acoustic radiator, 14 is a flexible connector, 51 is an inner cylinder of the acoustic radiator, 52 is also an outer cylinder, 61, 62
Fly electrodes, 63 and 64 are electrical terminals.

Claims (1)

[Claims] 1 A cylindrical piezoelectric transducer and a cylindrical acoustic radiator are arranged in series so that their central axes coincide, and the cylindrical piezoelectric transducer and the cylindrical acoustic radiator are coupled by a flexible connector. An omnidirectional underwater ultrasonic transducer characterized by: